Currently, for example, a cellular communication function is not only widely used for voice communication and data communication of mobile telephones and smartphones, but is also widely used by devices for machine type communication (also referred to as MTC devices). The number of communication terminals (referred to as UEs (User Equipment) or communication terminals below) including the MTC devices is increasing.
Users and applications (referred to as application servers below) operated by the users need both a communication method which performs activation from a MTC device side, and a communication method which activates the MTC device from a network side. The communication method which activates the MTC device from the network side includes triggering. This triggering is performed to activate a MTC device from the MTC application server via a network and establish communication connection.
Non-Patent Literature 1 proposes a plurality of methods for triggering a UE (MTC device). One of the plurality of methods is a method for triggering a UE (MTC device) from an external application server (AS) via a network node such as a MTC server (SCS: Service Capability Server) or a MTC-IWF (MTC-Interworking Function).
Non-Patent Literature 2 proposes a mechanism which monitors a quantity or a rate of triggering requested from a MTC server to a MTC-IWF and, when a total rate of trigger request from all SCSs, the total rate being in specific MTC server or specific MTC-IWF, exceeds a threshold, stops a triggering procedure, or suppresses triggering of a specific type to avoid situations of network congestion caused by very frequently executing triggering and an increase in battery consumption of the MTC device.
More specifically, the application server (AS) requests transmission of a device trigger request (also referred to as a trigger request below) to a MTC server (SCS: Service Capability Server), and the MTC server having received this request transmits the device trigger request to a MTC-IWF (Interworking Function which is also referred to as the IWF below).
The MTC-IWF having received the device trigger request executes necessary check, and performs processing for transmitting the device trigger to a UE.
In addition, the necessary check performed by the MTC-IWF is authorization of a transmission source MTC server. Further, the MTC-IWF checks load control of the trigger request received from the MTC server (whether or not a transmission count (submission quota) does not exceed a predetermined value, whether or not a transmission frequency (submission rate) of the trigger request does not exceed a predetermined value and whether or not a processing load of the MTC-IWF is an overload). When the transmission frequency of the trigger request exceeds the predetermined value, the MTC-IWF transmits to the MTC server a device trigger response (or a device trigger confirmation message which is referred to as a trigger response below) including a value (cause value) indicating that the device trigger cannot be transmitted due to a load control problem (reason of failure). Meanwhile, when no problem is found during the check, an inquiry is sent to a HLR/HSS (Home Location Register/Home Subscription Server which is a HSS) to obtain subscription information (subscriber information which is referred to as UE information below) for UE included in a response, and confirm contents of the subscription information as to whether or not the response indicates an error.